Mr. Teschemacher on Chromate of Silver. 345 



powder (unbruised), tlie wire of communication witli the well 

 was then fastened to the bottom of the brass stem. Being so 

 circumstanced, and whilst the charge in the great cylinder and 

 wire was continually kept up by the motion of the wheel, the 

 top of the cartridge was brought so near to the drums as fre- 

 quently to touch the metal. In this situation a small faint 

 luminous stream was observed between the top of the car- 

 tridge and the metal drum. Sometimes this stream would set 

 fire "to the gunpowder at the instant of the application ; at 

 others, it would require half a minute, or more, before it took 



effect." p. 75. 



I must now beg to call upon Mr. Sturgeon to verify his 

 assertion, by giving a reference to any electrical experiment 

 which either Dr. Watson or Mr. Wilson made with a wooden 

 point. 1 am, Gentlemen, your obhged servant, 



Hereford, Jan. 1 1, 1827. ThomaS Howldy. 



LXVIII. OnChromatc of Silver. i?j/iV/?-.E.F.TESCHEMACHER. 



To Richard Phillips, Esq. 

 Dear Sir, 



1BEG to hand you herewith a small quantity of crystallized 

 chromate of silver, obtained by allowing a solution of chro- 

 mate of potash (after separation of the precipitate occasioned 

 by nitrate of silver) to evaporate spontaneously : at the end of 

 te'n days these crystals were deposited at the bottom ot the 

 vessel." The crystals have a strong metallic lustre, and are 

 of a deep red colour by transmitted light, much resembling 

 native red silver. They are insoluble either in cold or hot 

 water. The primitive form appears to be a doubly oblique prism 

 of the following measurements, taken by Dr. Wollaston's re- 

 flective goniometer from very brilliant natural planes. 



Pen T . . . 123° 



Pon M . . 101° 05' 



M on T. . . 69° 55', or on T' 110° 05' 

 On platina wire before the blowpipe it gives a 

 deej) emerald green glass. On charcoal the sil- 

 ver is reducetl, appearing in small globules on 

 the surface of the chromic oxide. That this substance is a bi- 

 chromate of -silver, I have proved by directly combining the 

 chronuUe with an additional portion of chromic acid. 

 I am, dear sir, yours, &c. 

 Barnsbury, Maixh 13, 1827. E. F. TeSCHEMACHER. 



New Series. Vol. 1. No. 5. Mai/ 1827. 2 Y LXIX. On 



